1. Field of the Invention
The present invention relates to a cam apparatus using an electromagnet and gears for decelerating a motor.
2. Description of the Related Art
Recently, many apparatuses including tape recorders and disc mounting apparatuses have been developed which are electromagnetically driven. Cam apparatuses using an electromagnet and gears for decelerating a motor are generally used as such an electromagnetic driving mechanism.
Briefly referring to FIGS. 10 through 16, a conventional cam apparatus 50 will be described.
FIGS. 10 through 12 are plan views of the cam apparatus 50 each illustrating a step of operation; and FIGS. 13 through 15 are plan views of the cam apparatus 50, in which a cam gear 31 is shown as being transparent in order to clearly show positional relationship between the cam gear 31 and a lever 37 in each of the steps of operation shown in FIGS. 10 through 12. FIG. 16 is a cross sectional view of the cam apparatus 50 viewed along the section line 16--16 in FIG. 10.
The cam apparatus 50 includes the cam gear 31 including a toothless area 40 having no teeth, a driving gear 32 for driving the cam apparatus 50, a lock lever 33, and a lever 37. The lock lever 33 is biased counterclockwise around a shaft 39 by a spring 34. An end 43 of the lock lever 33 is in engagement with a projection 41 of the cam gear 31 so that the toothless area 40 can be opposed to the driving gear 32. The other end 44 is in engagement with a movable piece 36 of an electromagnet 35. Although not shown, the driving gear 32 is driven by a motor through a deceleration mechanism. The driving gear 32 is intended to rotate counterclockwise as is shown by arrow m in FIG. 10 when the motor is turned "ON".
As is shown in FIGS. 13 through 15, the lever 37 is rotatable around a shaft 45 which is concentric with the driving gear 32. As is also shown in FIG. 16, the lever 37 has a projection 46 at an end thereof, and the projection 46 is in engagement with a cam groove 47 provided at a rear surface of the cam gear 31. When the cam gear 31 pivots clockwise, the lever 37 is also intended to pivot through the engagement of the projection 46 along the cam groove 47. By such pivoting, the head of the tape recorder is moved up and down or the driving of the disc mounting apparatus is switched over.
Although the lever 37 rotates around the shaft 45 which is concentric with the driving gear 32 in FIGS. 13 through 15, the lever 37 may rotate around any other point.
The cam apparatus 50 having such a structure operates in the following manner:
In FIG. 10, the cam gear 31 stops with the end 43 of the lock lever 33 engaging the projection 41 of the cam gear 31 by the biasing force of the spring 34. The toothless area 40 of the cam gear 31 and the driving gear 32 are opposed to each other. When the electromagnet 35 is turned ON to pull the movable piece 36 leftward in FIG. 10, the lock lever 33 pivots clockwise around the shaft 39 against the force of the spring 34. Therefore, as is shown in FIG. 11, the end 43 of the lock lever 33 is released from the projection 41 of the cam gear 31. Then, the cam gear 31 rotates clockwise as is shown by arrow n in FIGS. 11 and 12 by the biasing force of the lever 37 which will be described later in detail. As a result, teeth 42 of the cam gear 31 and the driving gear 32 engage each other as is shown in FIG. 12. The cam gear 31 keeps rotating until the next toothless area is opposed to the driving gear 32, namely, until the end 43 of the lock lever 33 engages the next projection 41.
While the cam apparatus 50 is in the state illustrated in FIG. 10, the projection 46 is engaged with the cam groove 47 of the cam gear 31 as is shown in FIG. 13. The lever 37 is biased clockwise by a spring 38. By this biasing force of the lever 37, the cam gear 31 rotates clockwise. When the electromagnet 35 is turned ON, the teeth 42 of the cam gear 31 engage the driving gear 32 as is mentioned above and also illustrated in FIG. 12. During the engagement of the driving gear 32 and the teeth 42, the lever 37 pivots through the engagement of the projection 46 along the cam groove 47 in the cam gear 31 as is shown in FIG. 14. When the next toothless area is opposed to the driving gear 32, the lever 37 stops in the state of being biased counterclockwise by the spring 38 as is shown in FIG. 15. In this manner, each time the electromagnet 35 is turned ON, the lever 37 pivots between the two positions illustrated in FIGS. 13 and 15.
FIG. 17 is a general cam diagram, which illustrates the relationship between the rotation angle of the cam gear and a distance by which the projection of the lever travels. At point a, the cam gear 31 is locked as is illustrated in FIGS. 10 and 13. At point b, the driving gear 32 and the teeth 42 of the cam gear 31 start engaging each other as is shown in FIG. 11. At point c, the cam gear 31 is locked again as is illustrated in FIG. 15. Point d is a middle point of the movement of the lever 37. As the lever 37 moves farther from point d in either direction, the lever 37 is biased toward point d with a stronger force. At point e, the lever 37 is away from the starting point thereof at point a by a maximum distance. After point e, the cam gear 31 rotates by sliding of the projection 46 along a slanting portion of the cam groove 47 even without the force of the driving gear 32 until the projection 46 reaches point d. From point b to point f, the teeth 42 and the driving gear 32 are in engagement with each other, and the cam gear 31 rotates by the driving force of the driving gear 32. From point f to point g, the driving gear 32 is opposed to the toothless area 40, and the cam gear 31 rotates by the sliding of the projection 46 along the cam groove 47. From point g to point i, the driving gear 32 is again in engagement with the teeth 42, and the cam gear 31 rotates by the driving force of the driving gear 32 through point h at which the lever 37 is away from point e by a maximum distance. At point i, the driving gear 32 is disengaged from the teeth 42, and at point a, the cam gear 31 is locked again as is shown in FIGS. 10 and 13. Since the cam gear 31 rotates by the sliding of the projection 46 along the cam groove 47 until the driving gear 32 comes out of engagement with the teeth 42, the cam gear 31 would rotate 360.degree. without the engagement of the end 43 of the lock lever 33 and the projection 41 of the cam gear 31.
The above-described conventional cam apparatus 50 has the problem of generating noise. The noise is generated, for example, when the driving gear 32 engages the teeth 42 (FIG. 11) or when the projection 46 of the lever 37 slides along the cam groove 47 in acceleration.